1. Field of the Invention
This invention relates to an electric heating appliance, and more particularly, an electric heating appliance made so that the electric potential of a heater circuit becomes negative with respect to ground irrespective of the direction of insertion of a power source plug.
2. Description of the Prior Art
It has been known that, when an electrode kept at a negative potential is placed near a human body, a stiff shoulder healing effect can be obtained. Attempts to incorporate such a remedial appliance into an air-conditioner have heretofore been made.
For example, there are conventional techniques, which are disclosed in Japanese patent application Kokai publication No. 62-74373, for generating heat in a positive cycle of an AC power source, and insulating a heating circuit from the power source and providing this insulated heating circuit with negative electric potential in a negative cycle thereof. As shown in FIG. 4 of the accompanying drawings, the circuit disclosed in the above publication has a heater circuit consisting of an electric heater 1, an electric power controlling rectifying device 2 composed of SCR, and a temperature fuse 4, a main current circuit consisting of an insulating switch element (SCR) 8 for insulating the heater circuit from a commercial power source 6 in a negative cycle, and a diode 10, and a power source circuit for a control circuit 14, which consists of an insulating transformer 12, and the commercial power source 6 to which the insulating transformer is connected in parallel. The reference numeral 16 denotes a transformer for operating the insulating switch element 8 through the same transformer 16, a diode 17 and a resistor 18. The circuit of FIG. 4 is provided with a heat-sensitive layer 20 the impedance of which varies with temperature, and a signal line 22 for detecting the variations of impedance of this heat-sensitive layer 20, the signal line 22 being adapted to detect the temperature of the heat-sensitive layer 20 and apply a temperature signal to the control circuit 14 and a resistor 24 for melting the temperature fuse 4.
The condition of variations of electric potential in the case where a high-voltage generating circuit shown in the above publication is connected to the circuit of FIG. 4 will be described with reference to FIG. 5.
First, the circuit of FIG. 4, in which a grounding electrode E is connected as shown by a solid line, will be described. In this case, a circuit on the side of the anode of the electric power controlling rectifying element 2 is connected to the side of the grounding electrode, and the grounding electrode is set to zero volts. Consequently, in a negative cycle of the commercial power source, the insulating switch element 8 and electric power controlling rectifying element 2 are turned on, and, in a positive cycle thereof, the electric power controlling rectifying element 2 is turned off. The negative electric potential shown in the upper part of FIG. 5 is then supplied from a high negative electric potential generating circuit (not shown) connected to a cathode line in the negative electric potential insulating switch 8. In a negative cycle of the commercial power source 6, an electric current is supplied to the electric heater 1 to generate heat with the voltages at an a-portion of the electric heater 1, a central b-portion thereof and a c-portion thereof dropping to zero electric potential, negative electric potential of 1/2 of a peak level, and a peak negative electric potential, respectively, based on the ground potential.
When the electric power controlling element 2 is off, the grounding electrode E is set to zero volts. In the positive cycle of the commercial power source, the diode 10 stops the electric current, so that the electric current does not flow from the electric heater 1 to the grounding electrode E. Moreover, the insulating switch element 8 is turned off to insulate the electric heater 1 from the grounding electrode E. Accordingly, the electric potential of the electric heater 1 becomes negative. When a high negative potential is supplied, the level of the negative potential of the electric heater 1 becomes higher. In the negative cycle of the commercial power source with the electric power controlling rectifying element 2 off, the electric potential at all of the a, b and c-portions is zero. In accordance with the above statement, positive electric potential does not occur at all when the grounding electrode E is connected as shown by a solid line.
The case where a grounding electrode E' is connected as shown by a broken line in FIG. 4 unlike the above-described case will be described. In a positive cycle of the commercial power source with the grounding electrode E' set to zero volts, the insulating switch element 8 is turned on. When the electric power controlling rectifying element 2 is on, the voltages at the a, b and c-portions of the electric heater 1 drop to a peak positive electric potential, positive electric potential of 1/2 of the peak level, and zero electric potential, respectively, as shown in the lower portion of FIG. 5, to be heated. When the electric power controlling rectifying element 2 is off, positive electric potential of the same level occurs in all of the a, b and c-portions.
In a negative cycle of the commercial power source with the grounding electrode E' set to zero volts, the diode 10 stops the electric current, so that the electric current does not flow from the heater 1 to the grounding electrode E. Moreover, the insulating switch element 8 is turned off, so that the electric heater 1 is insulated from the commercial power source 6 with the electric potential thereof becoming negative.
As described above, when the grounding electrode E' is connected as shown by a broken line in FIG. 4, the electric potential of the electric heater 1 in a positive cycle of the commercial power source 6 becomes positive. Therefore, positive electric potential which is generally said to be harmful and useless to a human body works on the electric heater 1. Moreover, since a single-phase commercial AC power source does not have thereon any words about the grounded electrode, an ordinary man cannot use it with the direction of insertion of a power source plug limited.